Today it is well known to use homogenizers within the food processing industry. For instance, within the dairy industry homogenizers are used for dividing fat globules into minor parts in order to obtain a stable fat emulsion against gravity separation. In other words, by homogenizing milk one can avoid that a cream layer is formed on top of the milk product. Other reasons for homogenizing food products are to achieve a more appetizing colour, reduced sensitivity of fat oxidation, more full bodied flavor, improved mouthfeel and better stability of cultured milk products.
The homogenizer and the homogenizing process are further described in “Dairy Processing Handbook” published by Tetra Pak, hereby incorporated by reference.
Generally a homogenizer can be divided in two main parts, a pump forming a high pressure and a homogenizing device providing a gap through which the product is forced. Today, most often the pump is a piston pump with three to five pistons. The pump may be a double membrane diaphragm pump as described in the international publication WO2014/095898 by the applicant, hereby incorporated by reference. This type of pump is ideal for hygienic applications such as homogenizers, and utilizes a chamber formed between two membranes forming a seal between a liquid product, i.e. a hygienic side, and a hydraulic pressure source, i.e. a non-hygienic side. Such a pump is normally operated to increase the pressure from approximately 3 bar up to 250 bar during the course of each pump/suction stroke. The pressure in the pump chamber hus increases from a low pressure, such as 3 bar, to a high pressure, such as 250 bar in a periodical manner during operation. Even higher pressure may also be provided. Further to this, elevated temperatures up to 140° C. may be provided, especially if the pump is arranged adjacent to heat treatment equipment.
In order for a pump of the above kind to operate efficiently, smooth and with least wear it is important that the diaphragm stroke is synchronized with the piston stroke. The synchronization is made through balancing of the volume of hydraulic fluid, e.g. hydraulic oil, in the hydraulic system of the pump. An incorrect hydraulic fluid volume will lead to an unsynchronized relation between the motion of the diaphragm and the motion of the piston, which increases the risk of damage to the diaphragm due to collisions with the pump housing. If the hydraulic fluid volume is below a nominal value the diaphragm will, during a suction stroke, reach its rear turning point prior to the piston and as the piston continues backwards the diaphragm will collide with the rear wall of the diaphragm cavity in the pump housing. If the hydraulic fluid volume is instead above a nominal value the diaphragm will, during a pump stroke, reach its front turning point prior to the piston and as the piston continues forwards the diaphragm will collide with the front wall of the diaphragm cavity of the pump housing. The collisions lead not only to wear of the diaphragm, but also to unwanted vibrations and noise. Additionally, excess hydraulic fluid in the system will rapidly create a high pressure difference over the diaphragm, during the pump stroke, as the diaphragm reaches the front wall of the diaphragm cavity. This will cause fatigue to the diaphragm and considerably reduce its lifetime. In addition, if the hydraulic fluid volume is below or above the nominal value, the efficiency of the pump decreases, i.e. the volume of product being pumped per stroke will decrease.
One way of balancing the hydraulic fluid in a piston pump is to use valves, e.g. a release valve for releasing excess hydraulic fluid from the system and a replenishing valve for refilling hydraulic fluid if required. The valves are activated by the pressure level in the hydraulic system. However, valves have a physical reaction time. For example, if using a spring loaded, ball type as replenishing valve, the ball needs to be lifted from the valve seat and the spring needs to be compressed before the hydraulic fluid passage is open. These actions require mass to be accelerated, and after that the hydraulic fluid itself must be set in motion.
Another way of balancing the hydraulic fluid is to use a camshaft mechanism in order to refill hydraulic fluid and a release valve for excess fluid. Also in this case mass needs to be accelerated, and hence there is a reaction time to consider.
Therefore, at present, none of the above solutions have proven to be able to operate fast enough to be used for high speed applications. With high speed applications is meant applications in which the pump is to make more than one full stroke per second, e.g. operating at a frequency of about 2-4 Hz.